plzzzz help me with this prg any one ....urgent

[vikrant3mahajan]

hey guys any one plz help me i would be highly thankful...avtually i a m trying to read and write raw disk sectors using vc++.i am able to read properly but as i write i get an exception which i am not able to sort out..the problem is the bytes are written on destination but after writing the application gives exception plz help me out..exception is in the writefile function line

here goes the program

// cod.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include "cod.h"
//#include <iostream.h>
#include <winnt.h>
#include <Winbase.h>
#include <conio.h>
#ifdef _DEBUG
#define new DEBUG_NEW
#endif
#ifdef UNICODE
#undef UNICODE
#endif

// The one and only application object

CWinApp theApp;

//using namespace std;


        

        int _tmain(int argc, TCHAR* argv[], TCHAR* envp[])
{		
	
	DWORD bytesread;
	char hexcode[10];
	DWORD sector=0;
DWORD sectorN=1;

		char* buffer = (char*)malloc (512);
		
	int drive=0;
	HANDLE hDevice= CreateFileA("\\\\.\\N:",GENERIC_READ|GENERIC_WRITE, FILE_SHARE_READ | FILE_SHARE_WRITE,NULL, OPEN_EXISTING, FILE_FLAG_WRITE_THROUGH, NULL); 
	if (hDevice == INVALID_HANDLE_VALUE) 
        printf("Error");
	else
		printf("Success\n");

	SetFilePointer (hDevice,(sector*512), NULL, FILE_BEGIN); 
if (!ReadFile (hDevice, buffer, 512*sectorN, &bytesread, NULL) )
		 printf("unable to read");

for (int i=0; i<512; i++)
	{
		if(i%16==0)
			printf("\n");
printf("%02X ",buffer[i]&0xff);
	}



printf("\n");

for (int i=0; i<512; i++)
	{
buffer[i]=12;
}


SetFilePointer (hDevice, (sector*512), NULL, FILE_BEGIN); 
LPDWORD bytesN=0;BOOL h;


try{

h=WriteFile(hDevice,buffer,512,bytesN,NULL);   //this is the part where i am trying to write plz help 

}catch(CException *e){printf("exception");}



printf("\n\nWritten\n");


	for (int i=0; i<512; i++)
	{
		if(i%16==0)
			printf("\n");
printf("%02X ",buffer[i]&0xff);

	}
getch();
return 0;

}

EXCEPTION IT GIVES IS:


Unhandled exception at 0x7c811024 in cod.exe: 0xC0000005: Access violation writing location 0x00000000.



if it is unable to write then how can data be still written..


i had also attached the source file and the exception i get screenshot


help me out guys plzzzzzz